The present invention relates to a mechanical seal for preventing a fluid from leakage through rotary shaft portions. More particularly, the invention relates to an improvement in a mechanical seal which prevents the leakage of fluid when the pressurized sealed fluid is a liquid or a mixture of a gas and a liquid and the external fluid is a gas, generally ambient air.
In a mechanical seal of the above-mentioned kind, a seating ring on the stationary side which receives therethrough a rotary shaft is generally brought into slidable contact with a follower ring which is rotated together with the above rotary shaft, thereby avoiding leakage of the fluid from the outside of the sliding contact portion to the inside thereof. In order to enhance the sealing effect of the sliding contact surfaces in the conventional prior art, the pressure per unit area on the sliding contact surfaces is increased by enlarging the pressure of the follower ring against the seating ring. Or, as another measure, tight sealing surfaces are formed by selecting the material for both rings that are in contact with each other. However, the occurrence of coarsening and other changes, with the passage of time, in the sliding contact surfaces cannot be prevented. Especially, when the mechanical seal is used under severe conditions involving vigorous vibration and large temperature variation, such as those in a compressor for an automobile cooler, the fluid leakage soon becomes serious. Therefore, the proposal of a radical countermeasure has been eagerly desired.
As the fundamental measure for this sealing means, the inventors of the present application have invented a mechanical seal in which at least one of the sliding surfaces of a seating ring and a follower ring is provided with fine grooves having closed outside ends. This mechanical seal has been applied for a patent in the United States (U.S. patent application Ser. No. 895,072).
The invention of the above patent application is characterized in that at least one of the sliding surfaces is provided with fine grooves in certain shapes having closed outside ends. This depends upon the fact that the radial pressure against the leakage flow can be produced by utilizing the relative rotations of the sliding surfaces to the fluid that is held in the minute clearance between the sliding surfaces. It is considered that the effect of leakage prevention can be attained by the pumping action of the fine grooves with the rotation of the follower ring or by the centrifugal force that is exerted on the fluid that enters into the fine grooves when the grooves are formed on the side of the follower ring.
Meanwhile, as the result of further investigations, it has been understood that about the same sealing effect can also be expected when the fine grooves formed in the sliding surface of the follower ring are replaced by a plurality of holes. The holes are arranged on imaginary lines that are inclined rearwardly relative to the rotational direction of the follower ring. Furthermore, it has also been understood that, under the use conditions for the compressor of an automobile cooler, even when a plurality of these holes are formed regularly or irregularly in the inside portion of the sliding surface of the follower ring, about the same or a little less sealing effect can be obtained as compared with the case of the fine grooves. Further, the above-mentioned a little less sealing effect is still better than the sealing effect of the prior art devices. Especially, a very good sealing effect can be obtained during the high speed rotation of the follower ring.